1. Field of the Invention
The invention relates to a control system and a control method for a vehicle. More particularly, the invention relates to a control system and a control method for a vehicle that is capable of traveling by motive power from at least one of an internal combustion engine and a rotary electric machine, and that is equipped with an EV switch that allows selection of a travel of the vehicle in an EV mode in which priority is given to an EV travel of the vehicle that is performed by the motive power only from the rotary electric machine.
2. Description of Related Art
Some of the hybrid vehicles capable of traveling by motive power from at least one of an internal combustion engine and a rotary electric machine are equipped with an EV switch. The EV switch has functions as follows. That is, during an HV travel in an HV mode in which the hybrid vehicle travels by motive power from the internal combustion engine and the rotary electric machine, the travel mode can automatically transition to an EV travel in some cases depending on conditions, but in some other cases, the EV travel is preferentially selected when the EV switch is depressed, on condition that a predetermined condition regarding the state of charge of an electricity storage device, the vehicle speed, the temperature of the rotary electric machine, etc. is satisfied. Thus, the provision of the EV switch makes it possible to give priority to the EV travel by the operation of depressing the EV switch besides the automatic transition from the HV travel to the EV travel that is performed depending on conditions.
For example, Japanese Patent Application Publication No. 2009-248822 (JP-A-2009-248822) points out, with regard to a amount-of-stored-electricity control apparatus of a hybrid vehicle capable of traveling in the EV mode in which only the rotary electric machine is used as a drive force generation source, that while the charging control of a high-voltage battery is performed so that the amount of stored electricity of the battery is between a lower-limit amount of stored electricity above which the battery is not overdischarged and an upper-limit amount of stored electricity below which the battery is not overcharged, the travel distance that can be requested in the EV mode is restricted by the upper-limit amount of stored electricity of the high-voltage battery. According to this publication, an EV mode preparation start switch and an EV mode travel start switch are provided, and when the EV mode preparation start switch has been switched on and a requested EV-mode cruising distance has been input, a target amount of stored electricity corresponding to the input requested cruising distance is calculated. Then, if the calculated target amount of stored electricity is greater than the upper-limit amount of stored electricity, the calculated target amount of stored electricity is used to perform the charging control. Then, if the EV travel start switch is turned on, the EV mode travel is performed after it is checked that the state of charge is greater than or equal to the lower-limit amount of stored electricity.
Besides, Japanese Patent Application Publication No. 2008-137543 (JP-A-2008-137543) describes a control method for a hybrid vehicle in which when the EV switch is turned on, an electric motor-driven travel of the vehicle is permitted and an indicator is lighted on if a motor-driven travel permission condition that the remaining SOC value of the battery be greater than or equal to a threshold SOC value and the coolant temperature Tw be greater than or equal to a threshold value T1 is satisfied. Furthermore, according to this publication, when the motor-driven travel permission condition is not satisfied, a warning sound or a warning voice is output, and the condition that has not been satisfied is shown on a display. When the remaining SOC value is greater than or equal to the threshold SOC value, but is such a value that it can be predicted that the SOC value will reach the threshold SOC value if the motor-driven travel continues, or when the vehicle speed is less than or equal to an upper-limit vehicle speed threshold value that the motor-driven travel is stopped, but is such a value that it can be predicted that the vehicle speed will reach the upper-limit vehicle speed threshold value if the motor-driven travel continues, a display indication regarding a predicted stop of travel is produced.
Besides, Japanese Patent Application Publication No. 2007-238022 (JP-A-2007-238022) describes a control method of controlling the system start of a hybrid vehicle in a situation where quietness is required, for example, during midnight, early morning, etc. In this control method, if an EV signal that is an electric motor-driven travel signal is turned on and an indicator is lighted on, or if the signal is stored into a flash memory and then a brake pedal is depressed and a power switch is pressed and therefore a starting control routine is executed, an HV ECU receives the EV signal that is transferred thereto with an IG signal and a start signal, so that the EV travel can be performed immediately following the system start of the vehicle.
During a travel during which quietness is required, such as during midnight, early morning, etc., as mentioned in Japanese Patent Application Publication No. 2007-238022 (JP-A-2007-238022), a hybrid vehicle capable of traveling by the motive power only from the rotary electric machine when the user operates the EV switch can fully demonstrate the feature thereof.
By the way, in order to enable the vehicle to travel by the motive power only from the rotary electric machine, it is necessary to satisfy conditions, including, for example, a condition that the amount of stored electricity of an electricity storage device be sufficient, a condition that the electric power of the electricity storage device not be being consumed in a large amount for another purpose, a condition that the internal combustion engine not be presently needed for the travel of the vehicle, etc. Thus, it is not always possible to perform a transition to the travel of the vehicle only by the rotary electric machine when the EV switch is operated by a user. As stated in Japanese Patent Application Publication No. 2008-137543 (JP-A-2008-137543), if when the EV switch is depressed it is determined that the EV mode travel is not feasible, a display indication, for example, a message “EV mode request has been cancelled.” or the like, is produced by an appropriate display portion in a cabin of the vehicle. Thus, there can occur cases where although the user desires the EV mode travel, the desire cannot be accomplished, depending on the state of the vehicle.